Multimetal blind rivets and pulling stems

ABSTRACT

The use of high strength alloys in the art of blind riveting or riveting from one side only of a structure is made possible by novel combinations of rivet bodies and pulling stems. Pure titanium and titanium and other alloys are joined together to form the rivet body, while titanium alloys and other metals are joined together to form the pulling stem, by use of an integral joining process such as the friction welding process. With these combinations it is possible to utilize the great advantages of special alloys and other metals from the standpoint of strength at elevated temperatures and still make possible the formation of blind rivet heads. Similarly the fastening or plug section of the pulling stem is made of a different metal from the metal of the pulling section and is provided with a breakneck usual in the art of blind rivets and lockbolts.

United States Patent Gapp et al.

[1 1 3,685,391 1 Aug. 22, 1972 4] MULTIMETAL BLIND RIVETS AND PULLING STEMS [72] Inventors: Roland Howard Gapp, South Laguna; Marcos Alazraki, Orange; John Harper, Santa Ana, all of Calif. [73] Assignee: Textron, Inc.

[22] Filed: Feb. 16, 1970 [21] Appl. No; 11,771

Related US. Application Data [63] Continuation-in-part of Ser. No. 740,811, May

31, 1968, abandoned.

[52] US. Cl ..85/77 [51] Int. Cl ..Fl6b 19/10 [58] Field of Search ..85/77, 78

[56] References Cited UNITED STATES PATENTS 2,501,567 3/1950 Huck ..85/78 2,974,558 3/1961 Hodell 85/77 3,279,304 10/1966 Hopkins ..85/77 3,148,578 9/1964 Gapp ..85/77 FOREIGN PATENTS OR APPLICATIONS 1,010,802 1l/l965 Great Britain.....,. ..85/78 Primary ExaminerEdward C. Allen Attorney-George B. White [5 7] ABSTRACT The use of high strength alloys in the art of blind riveting or riveting from one side only of a structure is made possible by novel combinations of rivet bodies and pulling stems. Pure titanium and titanium and other alloys are joined together to form the rivet body, while titanium alloys and other metals are joined together to form the pulling stem, by use of an integral joining process such as the friction welding process. With these combinations it is possible to utilize the great advantages of special alloys and other metals from the standpoint of strength at elevated temperatures and still make possible the formation of blind rivet heads. Similarly the fastening or plug section of the pulling stem is made of a different metal from the metal of the pulling section and is provided with a breakneck usual in the art of blind rivets and lockbolts.

2 Claims, 9 Drawing Figures P'ATE'N'TEUAI BZZIHR 3.685391 SHEET 1 BF 2 INVENTORS ROLAND HOWARD GAPP MARCOS DAN/EL ALAZRAK/ JOHN HARPER ATTORNEY PATENTEDnuszz m2 SHEET 2 BF 2 Q Fig.9. //a' /16 Lii A INVENTORS ROLAND HOWARD GAPP MARCOS DAN/EL ALAZRAK/ JOHN HARPER ATTORNEY MULTIMETAL BLIND RIVETS AND PULLING STEMS This application is a continuation-in-part of copending application of the same applicants for Multimetal Blind Rivets and Pulling Stems, Ser. No. 740,81 1, filed May 31, 1968, and now abandoned.

BACKGROUND OF THE INVENTION The advantages of blind riveting or riveting from one side only of a structure by inserting a hollow rivet with a preformed head through a hole in the members to be riveted together and then forming a rivet head on the opposite side by means of a pulling stem is well known in the art. To be successful this type of rivet must be made of a material which is sufficiently malleable so that the blind head may be readily formed by the pulling process and yet have sufficient strength in shear and tension to hold the riveted parts together. In recent years the use of titanium, titamium alloys and other special alloys has found great favor where high strength and low weight are important. This is particularly true in the aircraft industry. It is even more important where elevated temperatures are involved as in supersonic aircraft where certain titanium alloys are especially in great favor.

Blind riveting has been used for many years in the aircraft and related industries, the metal used being various aluminum alloys and other malleable and readily formable material to permit ready formation of the blind head and still provide sufficient strength in the rivet. In the case of many alloys such as those of titanium, however, if an alloy having the required tensile and shear strength is used for the rivet body, it is virtually impossible to form a satisfactory blind head without splitting the rivet shell.

It is therefore an object of our invention to provide a blind rivet of high strength alloys such as those of titanium in which it would be possible to form a satisfactory head on the blind side.

It is another object of our invention to provide a pulling stem grooved suitably to interlock with a collar swaged therein and having a breakneck groove to break at a predetermined stress, the pulling section of the stem being of different metal than the part having the swaging grooves.

It is another object of our invention to provide a combination of rivet body and pulling stem of suitable construction to make possible the blind riveting of titanium and similar alloy rivets.

It is a general object of our invention to provide a combination of rivet body and pulling stem of suitable materials and construction to make possible the blind riveting of a wide variety of high strength alloy rivets.

SUMMARY We have discovered that by using pure titanium alloys and other special metals and alloys to form various sections of our rivet body as well as our pulling stem and joining these sections together by means of an integral joining process we are able to provide an unusual rivet which will give the high room and elevated temperature strength characteristics of certain titanium and other alloys and still enable us to form a blind head. Our construction relates to the rivet body itself as well as the pulling stem and the proper interaction between the two.

In the case of the rivet body, we may provide a tail section of one material and a head and shank section of another material and weld these together, for instance, by means of a friction welding process or other integral 5 joining processes. In the case of the stem, we provide a plug section of one material and a pulling section of another material and also join these integrally by a suitable joining process. By properly selecting the material, we are then able to form a suitable blind head on our rivet from the tail section as a result of proper interaction with the properly selected stem plug section, thus getting a resultant rivet having all the desired properties and over coming the objections set forth above. This will be evident from the description and the drawings which follow.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view illustrating a typical example of a blind rivet and pulling stem in an advanced step in the installation process.

FIG. 2 is a sectional view showing the completed rivet of FIG. 1.

FIG. 3 is a sectional view illustrating an example of a blind rivet of the bulbed head type and pulling stem at an advanced step in the installation process.

FIG. 4 is a sectional view showing the completed rivet of FIG. 3.

FIG. 5 is a section view of a bimetallic body of the rivet of out invention in combination with a unimetallic pulling stem.

FIG. 6 is a longitudinal view of a bimetallic pulling stem of our invention.

FIG. 7 is a sectional view of another embodiment of a bimetallic body of the rivet of our invention in combination with a unimetallic pulling stem.

FIG. 8 is a sectional view of a bimetallic body of the rivet of our invention in combination with a bimetallic pulling stem.

FIG. 9 is a sectional view of a bimetallic body of the rivet of our invention in combination with a trimetallic pulling stem.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring now particularly to FIG. 1 and FIG. 2 there is seen a conventional bind rivet having a preformed head 1, rivet body 2, blind formed rivet head 3 and locking collar 4. The pulling stem is comprised of body section 5 which serves to hold knurled or splined section 6 and adapter section 7 for connecting with a suitable pulling tool or mechanism. Plug section 8 of the pulling stem equipped with a tapered portion 9 and a wire drawing portion 10 which respectively serve to form the blind head 3 and expand rivet'body 2 into the holes in the members being riveted as shown in a manner more fully described in Gapp US. Pat. No. 2,931,532. After the stem is pulled to a predetermined position the locking collar 4 is set in place by means of a suitable tool as is well known to those skilled in the art and the stem body 5 fractures at a predetermined stress and location, which is predetermined by a usual breaking groove.

In FIG. 3 and FIG. 4 there is seen another embodiment of a blind rivet which is described more fully in Gapp US. Pat. No. 3,148,578. In this embodiment the blind head 3 is formed in the shape of a bulbed or mushroom head as shown by means of the special con struction of plug section 9a which is described as a bulb forming section in the above mentioned patent.

Our present invention is adapted to form rivets of either of the two types described above or of other types known in the art.

Referring now to FIG. 5 there is seen the combination of a rivet having a bimetallic body with a unimetal- Iic pulling stem. Here the 'pulling stem comprises a body section 5, a knurled or splined section 6, and an adapter section 7, as well as a plug section 8. As in the previous illustration, the tapered portion of the plug section 9 is also similar to that previously described and performs a similar function, except for the combinations of special materials as set forth below.

We have discovered that certain metals and alloys all having a high tensile and shear strength may be employed for the head and shank section 2b and combined at interface 2a after the manner of our invention with other ,metals and alloys having a high ductility and being readily formable to comprise the tail section 20 thus producing a highly superior rivet.

Materials used for the head and shank section 2b have a shear strength of up to 180,000 pounds per square inch, a tensile strength of up to 300,000 pounds per square inch at room temperature and an acceptable strength at temperatures as high as I ,00O F.

Materials used for the tail section 20 besides being ductile and readily formable should be compatible with the material used for head forming as described herein and also capable of joining integrally with the head and tail section by means of friction welding or other integral forming process at interface 2a.

Materials which we have discovered that may be combined to form the bimetal rivet of our invention are tabulated below in table I.

TABLE I Rivet Body Material Combinations Head & Shank Section 2b Tail Section In the case of the pulling stem we require a material which has a high tensile strength and is still compatible with the material used for the rivet sections as described herein. To accomplish this we may employ different combinations of material for the pulling section 8b and the plug section 8c. These we join at interface 8a by an integral forming process as in the case of the rivet itself described above. This is best seen in FIGS. 6 and 8. The interface is sufficiently firm to apply pulling stress until the stem breaks at said breaking grooves.

We have discovered further that superior results may be obtained insofar as the integral forming process is concerned by using the trimetallic embodiment for our pulling stem last seen on FIG. 9. Here we employ an intermediate section I] which forms interfaces Ila and 11b with opposite parts of plug'sections Ilc and 11:! respectively, said interfaces comprising integrally formed joints as described above. The material of section 11 is more readily joinable to the material of sections Ilc and 11d respectively than would be these materials to each other.

Materials which we have discovered that may be combined to form the stem of our invention are tabulated below in table I I.

TABLE II Stem Material Combinations as FS 60 Zirconium Alloy such as Zirconium 2 Vasco Max 300 Same as above AlSl 4340 Same as above Molybdenum Alloy such as Mo.5 Ti Pure Vanadium NOTE:

As used herein MP-35N is the designation used by Latrobe Steel Co. for its alloy consisting of approximately 35% nickel, 35% cobalt, 20% Chromium and 10% molybdenum.

Vasco 300 designates Vanadium Alloys Steel Co.'s alloy consisting of approximately 18% nickel, 9% cobalt, 0.5% molybdenum. 0.6% titanium, 0. I% aluminum and 0.02% carbon.

The chemical composition of materials represented by the other material symbols used herein may be found in the publication DMIC Memorandum 232 dated Feb. I, 1968, entitled Designations of Alloys for the Aerospace Industry (Revised) and published by Defense Metals Information Center, Battelle Memorial Institute, Columbus, Ohio 43201.

In connection with rivet bodies where the individual sections are composed of materials having substantially different chemical compositions, for instance the combinations hereinabove recited, the rivet body may be subjected to heat treatment after the sections are welded together, with the result that the head and shank material is hardened to a relatively high shear strength, while the tail material remains or is made appreciably lower in shear strength and with sufficient ductility to be readily formed or upset without cracking.

It was also discovered that the required union can be accomplished if the head and shank section of the rivet body is subjected to heat treatment and the tail section of the rivet body also subjected to heat treatment separately prior to welding so that said head and shank section is treated to have a relatively high shear strength and said tail section is pretreated so as to have appreciably lower shear strength and sufficient ductility to be readily formed or upset without cracking. When the sections are heat treated separately prior to welding it is possible to use materials of the same composition for both sections or of substantially different compositions for the two sections.

Examples of materials where the same material is used for both sections of the rivet body and may be heat treated as aforesaid are: Ti-6Al-4V, Beta lIl (Ti- 1 1.5 Mo-6Zr-4.5Sn), Ti-8Mo-8V-aFe-3Al, and Beta C (Ti-3Al-8V-6Cr-4Mo-4Zr).

Examples where the two sections of the rivet body are of different materials and are treated before welding are: Ti-6Al-4V for the head and shank section; and Pure Titanium, Ti-3Al-2.5V, Beta lIl (Ti-l 1.5 Mo-6Zr- 4.5Sn), Ti-8Mo-8V-2Fe-3Al, or Beta C (Ti-3Al-8V-6 Cr-4Mo-4Zr) for the tail section.

Further examples of materials of like or nearly like chemical composition heat treated to different conditions as separate parts prior to welding to form the rivet body are as follows:

Tail Section 6Al-4V titanium annealed 1325 Beta lll titanium solution treated l275l300 SMin. l" WQ-aged 1 100 4hrs l0", raised Head & Shank Section 6Al-4V titanium solution treated l625 1 hr 10* WO-aged l000 4hrs 10- AC Beta lll titanium (made by Crucible Steel) (nominal composition ll.5 Mo

6 Zr4.5 Sn) solution treated 1325-1350 min. WQ-aged 900 4 hrsv l0 AC to l 175lkhrs. [0- AC 8Mo8V-2FesAi(made by Timet) 8-8-2-3 titanium titanium solution treated I425 5 min. hot rolled, lO- WQ-aged 900 4hrs 10- AC straightened and ground Beta C titanium solution treated Beta C (made by Reactive Metals) titanium (nominal composition 3Al-8V- 10- is degree of vacuum expressed in Torr units.

We have discovered also that in addition to use of friction welding to form out multimetal rivets and stems, we may use also other forms of integral joining such as metallur bonding of the pressure, vacuum or diffusion type as well as fusion welding by use of electron or laser beams.

The adaptation of pulling stems to so-called lockbolts is well known in the art, such as the lockbolt shown in FIG. 1 of US. Pat. No. 3,180,0l7 granted on Apr. 27, 1965. The important feature is that the interface 8a or 11, be spaced from the breaking groove toward the adapter or pulling section 7 so that setting pull is exerted until after the plug or bolt section is interlocked with the swaged collar 4, and thus sufficient resistance is created to break the stem at the breaking groove.

We claim:

1. In a blind rivet comprising pulling stem and a hollow rivet body having a tail section, said pulling stern being extended through said hollow rivet body and having a former thereon to enlarge said tail section into a head when pulled thereinto, the improvement in said rivet body corn rising:

a head and s ank section and said head-forming tail section united end to end,

said head and shank section comprising a metal having a high shear and tensile strength,

said tail section comprising a ductile and readily formable metal,

said tail section and said head and shank section forming an interface therebetween,

the material composing said head and shank section being of substantially different chemical composition than the material comprising the tail section, said interface comprising an integral joint, said head and shank section comprising an alloy selected from the group consisting of Ti-6Al-4V, Ti-8Al-lMo-IV, Ti-6Al-6V-2Sn, and Ti-l3V- 1 lCr-3Al,

said tail section comprising a metal selected from the group consisting of titanium, vanadium, molybdenum Cb-lZr, Cb-752, Cb-lOW- l0Ta, Tantalum alloy FS 60 and zirconium 2.

2. The rivet of claim 1 in which said interface comprises a friction welded joint. 

1. In a blind rivet comprising pulling stem and a hollow rivet body having a tail section, said pulling stem being extended through said hollow rivet body and having a former thereon to enlarge said tail section into a head when pulled thereinto, the improvement in said rivet body comprising: a head and shank section and said head-forming tail section united end to end, said head and shank section comprising a metal having a high shear and tensile strength, said tail section comprising a ductile and readily formable metal, said tail section and said head and shank section forming an interface therebetween, the material composing said head and shank section being of substantially different chemical composition than the material comprising the tail section, said interface comprising an integral joint, said head and shank section comprising an alloy selected from the group consisting of Ti-6Al-4V, Ti-8Al-1Mo-IV, Ti-6Al-6V2Sn, and Ti-13V-11Cr-3Al, said tail section comprising a metal selected from the group consisting of titanium, vanadium, molybdenum Cb-1Zr, Cb-752, Cb-10W-10Ta, Tantalum alloy FS 60 and zirconium
 2. 2. The rivet of claim 1 in which said interface comprises a friction welded joint. 